de·crease • v. / diˈkrēs/ [intr.] become smaller or less in size, amount, intensity, or degree. ∎  [tr.] make smaller or less in size, amount, intensity, or degree: vitamin E has decreased cholesterol levels.• n. / ˈdēˌkrēs; diˈkrēs/ an instance or example of becoming smaller or less. ∎  the action or process of becoming smaller or fewer.PHRASES: on the decrease becoming less common or widespread.DERIVATIVES: de·creas·ing·ly / diˈkrēsinglē/ adv.

decrease grow less. XIV. — OF. de(s)creiss-, pres. stem of de(s)creistre (mod. décroître) :- Rom. *discrēscere, for L. dēcrēscere, f. DE- 6 + crēscere grow.
So decrease sb. XIV.